The Window Ball Grid Array, WBGA, semiconductor package becomes the major packages for IC memory devices where a WBGA package primarily comprises a substrate having window(s) to carry and electrically connect an IC chip and an encapsulant protecting the chip. However, at least a molding area on the bottom surface of the substrate is formed around the window where mold flash will easily occur. Since the window in the substrate of a conventional window-type BGA is a single central slot located at the center of the substrate, a distance is kept between the molding area and the external pads so that the mold flash can still be well controlled. However, in the new generation of window-type BGA, a plurality of small windows are disposed at the sides and at the corners of the substrate to increase the electrical routing density and to meet the requirement of finer pitches between electrical terminals, however, the problem of mold flash becomes worse due to smaller pitches between the molding area and the external pads. Eventually, the quality of the electrical connections will be affected by the mold flashes.
As shown in FIG. 1, a conventional window-type BGA package 100 primarily comprises a substrate unit 110, a chip 120, a plurality of electrical connecting components 130, and an encapsulant 140 where the substrate unit 110 is formed by singulating from a substrate strip. The substrate unit 110 has a die-attaching surface 111, an external surface 112, and a plurality of small windows 113 penetrating the substrate unit 111. As shown in FIG. 2, the small windows 113 are formed adjacent to the sides or to the corners of the substrate unit 110. A plurality of small window molding areas 114 are formed on the external surface 112 for the formation of the encapsulant 140 where the small window molding areas 114 surround the small windows 113 without extending to the corresponding sides nor corners of the substrate units 110. The substrate unit 110 further has a central slot 115. The external surface 112 further includes a bottom molding area 117 to surround the central slot 115. Furthermore, as shown in FIGS. 1 and 2, the substrate unit 110 further has a plurality of external pads 116 formed on the external surface 112 for disposing a plurality of external terminals 150 such as solder balls.
As shown in FIG. 1 again, a chip 120 has a plurality of bonding pads 121 disposed on its active surface and is attached to the die-attaching surface 111 of the substrate unit 110. The electrical connecting components 130 are formed by wire bonding to electrically connect the bonding pads 121 to the substrate unit 110 by passing through the small windows 113 and the central slot 115. The encapsulant 140 is formed on the die-attaching surface 111 and on the small window molding areas 114 and the bottom molding area 117 to encapsulate the chip 120 and the electrical connecting components 130. The molding area of the external surface 112 has to be controlled within the window molding area 114 and the bottom molding area 117. Since the conventional window BGA has many small windows 113, the mold flashes at the small window molding area 114 can easily contaminate the external pads 116 leading to poor electrical connections between the external terminals 150 and the external pads 116. Moreover, during singulation of substrate strip, the traces and solder mask at the sides or the corners of the substrate units are easily delaminated leading to poor package quality and reliability.
Furthermore, after die attachment and wire bonding processes, a molding process will be followed. A corresponding bottom mold chest has to be designed according to the locations and dimensions of the central slot 115 and the smaller windows 113 of a conventional window-type BGA. When the number of small windows 110 is increased, the cost of design the corresponding bottom mold chest will increase and the issue of mold flashed will become more serious.